Light sources and optical sheets are included in image display devices that emit images to observers, like liquid crystal displays, rear projection display devices, display devices using organic electroluminescence, and field emission displays (FEDs). Such an optical sheet is composed of a plurality of layers that have various functions for improving the quality of light emitted by the light source to offer the light to observers.
For example, such an optical sheet is disclosed in each of Patent Literatures 1 and 2.
The optical sheet (light control film) of Patent Literature 1 has transmissive regions that are arranged in a row along a sheet surface so as to be light-transmissive, and absorptive regions that are arranged in a row, each of which is between transmissive regions, so as to be light-absorptive. It is disclosed that a width at the narrowest region of a transmissive region and pitch of transmissive regions have a certain relationship.
The optical sheet of Patent Literature 2 includes an optical functional sheet layer that has prisms arranged in a row along a sheet surface so as to be light-transmissive, and light absorption parts arranged in a row, each of which is between prisms, so as to be light-absorptive. Thereby, an image light and outside light are reflected and absorbed, to improve the quality of the image light.
Here, interference fringes and scintillation (so-called glare) are sometimes generated in such an optical sheet, originating from a mode of arrangement of light absorption parts and light transmission parts alternately in a stripe pattern, light concentration due to control of the light, a mode of contact interfaces with other layers, etc. For this generation, Patent Literature 2 discloses that a surface of a base film is prepared to be a rough surface of no less than 0.1 μm in mean roughness (Ra), so that interference fringes can disappear.